As intelligent fluid, foam is widely used in the development field of oil and gas fields, covering various aspects, such as well drilling, well cementing, operation of oil and gas wells, well stimulation measures and increase in recovery efficiency. However, in the process of the application of foam to the development of the oil and gas fields, due to its thermodynamic instability, the foam is particularly easy to shatter in a flow process, so that profile control, blocking and other features of the foam are degraded greatly. Therefore, the key link of utilizing the foam to help the development of the oil and gas fields efficiently is to improve foam stability.
The booming of nano technology provides an extremely wide potential application scope ranging from electronics, communications, biology to energy sources for nano materials. As the nanoparticles have small sizes, great volume and surface effects, strong adsorbability and other features, people have proposed a method of utilizing the compounding of the nanoparticles and surfactants to collaboratively improve the foam stability. The method has the main advantages: the adsorption of the nanoparticles in a gas-liquid interface can inhibit the occurrence of the phenomena of coalescence and disproportionation of the foam; and the nanoparticles form bridging structures in a gas bubble liquid membrane to improve the foam stability.
As Zhang Shuiyan points out in her doctoral dissertation Foam Stabilized by Hectorite and HMHEC in Collaboration with Surfactants, hydrophilic hectorite particles and surfactant cetyl trimethyl ammonium bromide (CTAB) have a very good effect of stabilizing the foam through collaboration under the condition of an appropriate ratio, and a mechanism of stabilizing foam through collaboration is as follows: CTAB adsorbs on hectorite, so that the hydrophilicity of the hectorite particles is changed, thus making the hectorite particles have appropriate hydrophilicity and hydrophobicity and realizing the effect of stabilizing the foam through collaboration. Bernard P. Binks et al. have studied the mechanism of stabilizing the foam through collaboration of hydrophilic nano silica particles with surfactant didecyldimethylammonium bromide (di-C10DMAB), and pointed out that under the condition of an appropriate di-C10DMAB concentration, a wetting angle of the hydrophilic nano silica particles can be changed from 8° to 63°, thus increasing the hydrophobicity. Moreover, by exactly increasing their hydrophobicity to a certain extent, the two can collaborate to stabilize the foam [Soft Matter, 2008, 4(12): 2373-2382]. Sun Qian et al. have studied the mechanism of stabilizing the foam through collaboration of partially hydrophobic nano silica particles with surfactant lauryl sodium sulfate (SDS), and pointed out that the nano silica particles and SDS under the condition of an appropriate ratio can obviously improve the foam stability, thus increasing the recovery efficiency of crude oil [Energy & Fuels, 2014, 28(4): 2384-2394].
Chinese Patent CN102746841A discloses a compound foam system added with nanoparticles for oil and gas fields and a preparing method thereof. It discloses the method for preparing the compound foam system through the compounding of modified nano silica particles and lauryl sodium sulfate.
It can be found based on the above research that in the process of stabilizing the foam through collaboration of the nanoparticles with the surfactants, hydrophobicity and an electric feature of the particles are two important factors, and the hydrophobicity of the particles is more important. Only when the nanoparticles are in an appropriate hydrophobicity (the foam cannot be stabilized by extreme hydrophobicity either, and the wetting angle is preferred at 60°˜420°), can the foam be stabilized optimally. Therefore, people mainly employ compounding of the hydrophilic nanoparticles with the surfactants to change the hydrophilicity and hydrophobicity of the hydrophilic nanoparticles by the adsorbing of the surfactants on the surface of the hydrophilic nanoparticles, thereby obtaining a stable foam system. The method of compounding the hydrophobic nanoparticles with the surfactants to reduce the hydrophobicity of the hydrophobic nanoparticles and enhance the foam stability is rarely employed, which is mainly caused by the fact that when the hydrophobic nanoparticles are compounded with the surfactants, due to the hydrophobicity of the hydrophobic nanoparticles, there is no way to form a dispersion solution of the hydrophobic nanoparticles and the surfactants, and further there is no way to compound and stabilize the foam. In order to form the dispersion solution of the hydrophobic nanoparticles and the surfactants, Chinese patent CN102746841A employs the method of adding absolute ethyl alcohol as an additive. But when the amount of the added absolute ethyl alcohol is less, it is particularly easy for the nanoparticles to produce coalescence in the dispersion solution, which then influences the foam stabilizing effect, increases the amount of use, and virtually increases a production cost. When the amount of the added absolute ethyl alcohol is more, the absolute ethyl alcohol is an antifoam agent, and thus loses the foam stabilizing effect.
Therefore, whether it is possible to find an appropriate method to disperse the hydrophobic nanoparticles into water to form a compounding system with the surfactants so as to increase the utilization efficiency of the nanoparticles and lower the production cost becomes very important for providing feasibility for popularizing the application of the nanomaterials in the development of the oil and gas fields.
Chinese Patent CN103127744A discloses a method of transferring oil phase nanoparticles into a water phase, and discloses the forming of an oil-in-water microemulsion by means of ultrasonic emulsification, wherein the microemulsion is evaporated and dried to get stabilizer-nanoparticle compounded dried jelly, and then polar solvents that can dissolve stabilizers are added into the nanoparticle compounded dried jelly, thereby realizing the goal of dispersing the nanoparticles into the polar solvents. In this method, the nanoparticles need to be coated with oleic acid or oleylamine, and are then dispersed in volatile non-polar organic agents, and additionally there is a need for adding additives such as absolute ethyl alcohol and stabilizers such as polyvinylpyrrolidone. The method of dispersing the nanoparticles into the water phase can not realize the goal of making use of the surfactants to regulate the hydrophilicity and the hydrophobicity of the nanoparticles within a rational range and then realizing the effect of foam stabilizing. The main goal of the patent is to disperse nanoparticles synthesized in the oil phase into the water phase to increase an application range, but in the patent the compounding system of the nanoparticles and the surfactants is not considered to be dispersed into the water phase.